Bi-directionally movable platform control

ABSTRACT

Apparatus for regulating the position of a platform upon which sheets of material are stacked is provided in accordance with the teachings of the present invention. Direction determining means is adapted to produce first and second signals for driving said platform in first and second directions, respectively. The assumption by said platform of an extreme first position is sensed by first sensing means. First means coupled to said first sensing means is responsive to the energization of a selecting switch to actuate the direction determining means to produce said first signal when the platform is not in its extreme first position. Second means is selectively responsive to the deenergization of the selecting switch, to signals representing the operating conditions of the apparatus adapted to operate upon said sheets of material and to a signal generated in response to a predetermined operator-initiated action to produce said second signal. Drive means, including drive control means, responds to the produced first and second signals to move the platform to its extreme first position and to a proper sheet feeding position, respectively.

Reehil BI-DIRECTIONALLY MOVABLE PLATFORM CONTROL Oct. 30, 1973 57' ABSTRACT [75] Inventor; Edward (LReehfl Henrietta Apparatus for regulating the position of a platform upon which sheets of material are stacked is provided Asslgneei xerox Corporation Stamford in accordance with the teachings of the present inven- Conntion. Direction determining means is adapted to pro- [22] Filed: 30, 1971 duce first and second signals for driving said platform in first and second directions, respectively. The as- PP N05 214,299 sumption by 'said platform of an extreme first position is sensed by first sensing means. First means coupled 52 us. 01. 271/155 said first sensing means is rsslmsi"e the energi- [51] Int. Cl B65h 1/18 Zation of 3 Selecting switch to actuate direction [58] Field of Search 271/62 R, 62 B, 39, tsm'ining means Produce said first slgnal when 271/40 30, 31, 43 platform is not in its extreme first position. Second means is selectively responsive to the de-energization [56] References Cied of the selecting switch, to signals representing the op- UNITED STATES PATENTS erating conditions of the apparatus adapted to operate upon said sheets of material and to a signal generated 3,072,398 1/1963 Cozad et a1. 271 62 R in response to a predetermined eperateeinitiated giii zi s fg if" tion to produce said second signal. Drive means, in- 2:92l:788 1 1960 Lawrence 271/62 R cludmg dnve means responds to Pmduced first and second signals to move the platform to its ex- Pn-mary Examiner Evon Blunk treme first position and to a proper sheet feeding posi- Assistant Examiner-Bruce l-l. Stoner, Jr. respect'vely' Attorney-James J. Ralabate et al. I 13 Claims, 2- Drawing Figures L//' //09 Machine not 4 AND printing Time cut "(1/4 1 l ///2 s 1 AND m INV UP/DN h FF a OR AND R 0 AND AND ON film ma UP .125

Patented Oct. 30, 1973 3,768,806

2 Sheets-Sheet l Patented Oct. 30, 1973 2 Sheets-Sheet 2 come m3 NDx E a o 0E2. v= 9.15.5

BI-DIRECTIONALLY MOVABLE PLATFOR M CONTROL This invention relates to apparatus for regulating the movement of a bi-directionally movable platform, and more particularly, to apparatus for regulating the movement of a platform upon which sheets of material are stacked, which sheets are adapted to be fed through an electrostatic reproduction machine.

In the practice of xerography as described in US. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material affixed to 'a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic plate is electrostatically charged uniformly over its surface and then exposed to a light pattern of the image being reproduced to selectively dissipate the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern in conformity with the configuration of the original light pattern.

The electrostatic latent image may then be developed by contacting it with a finely divided electrostatically attractable material, such as a resinous powder. The powder is held in the image areas by the electrostatic fields on the layer. Where the field is greatest, the greatest amount of material is deposited; and where the field is least, little or no material is deposited. Thus, a viewable powder image is produced in conformity with the light image of the copy being reproduced. The powder is subsequently transferred to a sheet of paper or other support surface and suitably fused to thereby form a permanent print.

It is contemplated that the sheets of material to which the powder image is transferred be fed through the electrostatic reproduction machine in timed relation to the movement of the xerographic plate. Typical sheet feeding apparatus is disclosed in US. Pat. No. 3,661,452 claimed May 9, 1972 and assigned to Xerox Corporation, the assignee of the present invention. It has been suggested that such sheet feeding apparatus be supplied with sheets of material that are supported in a stack-like configuration on a movable platform. The platform is preferably driven in first and second directions by suitable drive means such that a first extreme position may be assumed and a proper sheet feeding position may be assumed. In the latter position, the sheets stacked on the platform may be fed in a successive manner to the sheet transport mechanism. The platform is adapted to be driven through positions intermediate the first extreme position and the proper sheet feeding position.

In the electrostatic reproduction machine with which the aforementioned platform finds ready application, use is made of the first extreme position to re-supply the platform with sheets of material, to vary the nature of such sheets of material or to effect other desired operator-initiated functions. When the platform assumes its first extreme position, normal operation of the electrostatic reproduction machine is impeded because thesheets of material cannot be properly supplied to the sheet transport mechanism. Accordingly, it is preferred to maintain the platform in its proper sheet feeding position at all times except during the performance of certain operator-initiated functions. Moreover, it has been found necessary to provide against operations inadvertently initiated by an operator or, once initiated, prematurely abandoned. Furthermore, precaution must be taken to avoid the displacement of the platform from its proper sheet feeding position for an excessive duration of time. In addition, movement of the platform should be restrained during those conditions presenting a substantial hazard to the safety of an operator.

Therefore, it is an object of the present invention to provide apparatus for regulating the position of a platform upon which sheets of material are stacked.

It is another object of the present invention to provide control apparatus for preventing the movement of a platform to a first extreme position in response to action inadvertently initiated by an operator.

A further object of this invention is to provide platform movement control apparatus requiring the continuous energization of a manually operable selecting switch to effect the movement of a platform to a first extreme position.

Yet another object of the present invention is to provide control apparatus for use in an electrostatic reproduction machine wherein a platform is automatically returned to a proper sheet feeding position after being displaced therefrom for a determined duration.

An additional object of this invention is to provide a platform for use with sheet feeding apparatus wherein said platform is normally biased to assume a proper sheet feeding position.

A still further object of the present invention is to provide control apparatus for restraining movement of a platform during potentially hazardous conditions presented by the opening of a platform access door.

Various other objects and advantages of the invention will become clear from the following detailed description ofan exemplary embodiment thereof, and the novel features will be particularly pointed out in connection with the appended claims.

In accordance with this invention, there is disclosed apparatus for regulating the position of a platform upon which sheets of material are stacked, including direction determining means for producing first and second signals to drive said platform in first and second directions, respectively; first sensing means for sensing the assumption by said platform of an extreme first position; first means coupled to said first sensing means and responsive to the energization of a selecting switch to actuate said direction determining means to produce said first signal when said platform is not in its extreme first position; second means selectively responsive to the de-energization of the selecting switch and to signals representing the operating condition of apparatus adapted to operate upon said sheets of material to actuate said direction determining means to produce said second signal; and drive means responsive to said first and second signals to effect the movement of said platform to its first extreme position and to a proper sheet feeding position, respectively. It is a feature of the present invention to provide additional means responsive to the occurrence of a potentially hazardous condition to inhibit the application of said first and second signals to said drive means.

The invention will be more clearly understood by reference to the following detailed description of an exemplary embodiment thereof in conjunction with the accompanying-drawings in which:

FIG. 1 is a schematic sectional view of an electrostatic reproduction machine embodying the principles of the invention; and

FIG. 2 schematically illustrates a movable platform upon which sheets of material to be utilized by the electrostatic reproduction machine are stacked, and the control means therefor.

For a general understanding of the illustrated copier/reproduction machine in which the invention may be incorporated, reference is had to FIG. 1 in which the various system components for the machine are schematically illustrated. As in all electrostatic systems, such as a xerographic machine of the type illustrated, a light image of a document to be reproduced is projected onto the .sensitized surface of a xerographic plate to form an electrostatic latent image thereon.

electrostatically transferred to a support surface and fixed by a fusing device to cause the powder image to adhere permanently to the support surface.

In the illustrated machine, a document D to be copied is placed upon a transparent support platen P fixedly arranged in an illumination assembly, generally indicated by the reference numeral 10, positioned at the left end of the machine. Light rays from an illumination system are flashed upon the document to produce image rays corresponding to the informational areas. The image rays are projected by means of an optical system onto the photosensitive surface of a xerographic plate in the form of a flexible photoconductive belt 12 arranged on a belt assembly, generally indicated by the reference numeral 14.

The belt 12 comprises a photoconductive layer of selenium which is the light receiving surface and imaging medium for the apparatus, on a conductive backing.

The surface of the photoconductive belt is made photosensitive by a previous step of uniformly charging the same by means of a corona generating device or corotron 13.

The belt is journaled for continuous movement upon three rollers 20, 21 and 22 positioned with their axes in parallel. The photoconductive belt assembly 14 is slidably mounted upon two support shafts 23 and 24 with the roller 22 rotatably supported on the shaft 23 which is secured to the frame of the apparatus and is rotatably driven by a suitable motor and drive assembly.

(not shown) in the direction of the arrow at a constant rate. During exposure of the belt 12, the portion exposed is that portion of the belt running between rollers and 21. During such movement of the belt 12, the reflected light image of such original document positioned on the platen is flashed on the surface of the belt to produce an electrostatic latent image thereon at exposure station A.

As the belt surface continues its movement, the electrostatic image passes through a developing station B in which there is positioned a developer assembly generally indicated by the reference numeral 15, and which provides development of the electrostatic image by means of multiple brushes 16 as the same moves through the development zone. Y

The developed electrostatic image is transported by the belt to a transfer station C whereat a sheet of copy paper is moved between a transfer roller and the belt at a speed in synchronism with the moving belt in order to accomplish transfer of the developed image solely by I meral 18 to. thedeveloped image on the belt at the sta- 7 tion C. 1

After the sheet is stripped from the belt 12, it is conveyed into a fuser assembly, generally indicated by the reference numeral 19, wherein the developed and transferred xerographic powder image on the sheet material is permanently affixed thereto. After fusing, the finished copy is discharged from the apparatus at a suitable point for collection externally of the apparatus.

Further details regarding the structure of the belt assembly 14 and its relationship with the machine and support therefor may be found in the 'copending Application Ser. No. 102,312 assigned to Xerox Corporation, the assignee of the present invention.

Referring now to FIG. 2, there is schematically illustrated a movable platform upon which sheets of copy paper are stacked and adapted to be fed to the aforementioned sheet transport mechanism. Apparatus for controlling the movement of the platform-is also illustrated. More particularly, the movable platform is included in an elevator assembly comprised of platform 101, and driving means 104. The platform 101 is adapted for bi-directional movement and serves as a support for sheets of copy paper 102. Each of the sheets is capable of receiving a developed electrostatic image transferred thereto and, therefore, may comprise any suitable support surface such as plastic, glass, paper, or the like. It will be assumed, for the purpose of the present explanation, that each sheet is comprised'of paper. I

The platform 101 is adapted to be driven in an upward and downward direction for a purpose soon to be described, and is coupled to driving means 104 by any conventional positioning means, generally indicated at 103. Driving means 104 may comprise an electric motor, such as a synchronous motor, coupled via a conventionalv coupling device 105 to positioning means 103. The latter ishere illustrated as a conventional pulley system comprised of pulley 126 about which is deployed cable 127, and winch 128 mechanically coupled to driving means 104 bycoup'ling device 105. The rotation of winch 128 is effective to wind the cable 127 thereon, thereby causing platform 101, which is coupled to the cable, to be driven in the upward direction. The platform is driven in a downward direction when the rotation of the winch is reversed. It may be appreciated that the continued rotation of winch 128 serves to again drive platform 101 in an upward direction. Means, not shown, are provided to arrest the operation of driving means 104 when the platform 101 attains a maximum upward position, thereby affording an overdrive protection to the platform and.the positioning means 103. Various other schemes may be employed to drive platform, 101 in an upward and downward direction.

The schematically illustrated elevator assembly is provided with an access door 107 that is normally maintained in aclosed position. Opening of the access door 107 permits an operator of the electrostatic reproduction machine to take appropriate action with regard to the sheets of material 102 stacked upon platform 101. Thus, additional sheets of material may be supplied or other sheets of material may be substituted once the access door 107 is opened. It is recognized that the opening of access door 107 presents a potentially hazardous condition to an operator and to the proper functioning of the electrostatic reproduction machine. Movement of platform 101 is, therefore, restrained when access door 107 is opened, as will soon be described. I

When platform 101 assumes a proper sheet feeding position, the top-most sheet stacked thereon admits of a position whereby it may be fed directly to the sheet transport mechanism, not shown herein. After a predetermined number of sheets have been thus fed, the platform 101 must be indexed upward to now allow the top-most sheet to be conveyed to the sheet transport mechanism. A suitable sensing transducer 123 is provided to ascertain when the top-most sheet is in a proper position for feeding to the sheet transport mechanism, and to produce a signal representative thereof. The transducer may comprise a spring-biased lever arm coupled to a mechanical switch whereby the angular rotation of the lever arm is a function of the position of the top-most sheet stacked upon platform 101. Thus, if the top-most sheet is not in position to be fed to the sheet transport mechanism, the lever arm will rotate, under the influence of the bias spring, to a position effecting the closure of the switch. The signal produced by transducer 123 is utilized by the platform control apparatus to be described below.

In the preferred embodiment of the present invention, it is desirable to enable an operator to perform various operations upon the sheets of material, i.e., replenish the supply or substitute therefor, when platform 101 obtains an extreme downward position. A suitable transducer 121 is, therefore, provided to sense when platform 101 obtains this position. Transducer 121 may comprise a conventional switch disposed in a fixed location and adapted to be contacted by platform 101 such that a representative signal is produced when the platform assumes its extreme downward position.

An exemplary embodiment of the illustrated appara, tus that serves to control the positioning of platform 101 comprises direction determining means 110, switch means 125, transducers 121-123 and drive control means 106. Drive control means 106 is responsive to first and second inputs applied thereto for regulating the operation of motor 104 coupled thereto. Hence, drive control means 106 is adapted to energize motor 104 in response to a first input applied thereto whereby motor 104 rotates in a first direction. Conversely, drive control means 106 is adapted to energize 'motor 104 in response to a second input applied thereto whereby motor 104 rotates in a second direction. If motor 104 comprises a synchronous motor, it is understood that drive control means 106 may supply the synchronous motor with alternating current admitting of a first or second phase in accordance with the application of a first or second input thereto; the first and second phases exhibiting a 180 phase relationship. Alternatively, if motor 104 comprises a dc motor, it should be recognized that drive control means 106 may supply the dc. motor with direct current admitting of a first or second polarity in accordance with the application of a first or second input thereto. Should motor 104 be capable of rotating in only a single direction, drive control means 106 may include a first clutch assembly operable in response to a first input applied thereto to engage a first gear mechanism whereby the platform 101 is driven in a downward direction, and a second clutch assembly operable in response to a second input applied thereto to engage a second gear mechanism whereby the platform 101 is driven in an upward direction.

A first input terminal of drive control means 106 is coupled to direction determining means 110 via coincidence means 112 and a second input terminal of drive control means 106 is coupled to direction determining means 110 via coincidence means 117. Each of coincidence means 112 and 117 is adapted to produce an output signal in response to the application of a predetermined signal at each input terminal thereof. Accordingly, coincidence means 112 and 117 may comprise conventional AND gates whereby a binary l is produced at the output terminal thereof when a binary l is supplied to each input terminal thereof. For the purpose of the present discussion, it will be assumed that a binary l is represented by a positive d.c. potential and a binary 0 is represented by ground potential. It is, of course, understood that the foregoing binary signals may be represented by any suitable voltage potentials. Similarly, coincidence means 112 and 117 may each comprise a conventional NAND gate wherein a binary 0 is produced at the output terminal thereof when a binary 1" is supplied to each input terminal thereof.

Direction determining means 110 is adapted to produce a first signal in response to a first set of conditions to drive platform-101 in a downward direction, and to produce a second signal in response to a second set of conditions to drive platform 101 in an upward direction. The produced first and second signals are applied to drive control means 106 via coincidence means 112 and 117 such that the actuation of drive control means 106 to supply motor 104 with energy may be inhibited during certain occurrences that will soon become apparent. Accordingly, a first output terminal of direction determining means 110 is coupled to an input terminal of coincidence means 112 and a second output terminal of coincidence means 110 is coupled to an input terminal of coincidence means 117. The direction determining means 110 comprises a conventional bistate device such as a flip-flop means having a set input terminal and a reset input terminal. The flip-flop means may be, typically, an R-S flip-flop, a Jl( flip-flop, or the like, wherein a first, or set, state is assumed in response to a binary l supplied to a set input terminal and a second, or reset, state is assumed in response to a binary l" supplied to a reset input terminal. Alternatively, the flip-flop means may comprise cross-coupled NOR gates or NAND gates, as is well known to those of ordinary skill in the art. The set input terminal of flip-flop means 110 is coupled to coincidence means 109 and the reset input terminal of flip-flop means 110 is coupled to OR circuit 115.

Coincidence means 109 is similar to aforedescribed Switch means 125 comprises a manually operable selectingswitch. The'switch means is coupled to a suitable source of energizing potential +V. It will soon become readily apparent that switch means 125 must be maintained in a continually energized condition to effect the lowering of platform 101 to its extreme downward position.

OR circuit 1 15 may comprise a conventional OR gate adapted to produce a binary 1 when at least one input terminal thereof is provided with a binary 1. Alternatively, OR circuit 115 may comprise a conventional NAND gate wherein a binary 1 is produced when at least one input terminal thereof is provided with a binary O. The OR circuit includes a first input terminal coupled to transducer 121 and a second input terminal coupled to terminal 114. The latter terminal is capable of being supplied with a signal derived from the electrostatic reproduction machine representative of the completion of an operating cycle thereby. OR circuit 115 further includes a third input terminal coupled to'switch means 124 and a fourth input terminal coupled to transducer 122. Switch means 124 is coupled to a suitable supply of energizing potential +V and is subject to manual operation whereupon an operating cycle is commenced by the electrostatic reproduction machine. The transducer 122, to which the fourth input terminal of OR circuit 115 is coupled, serves to sense the opened or closed condition of access door 107. Transducer 122 may, therefore, comprise a conventional switch disposed in afixed location relative to the access door and capable of producing a representative signal when the access door is opened.

Transducer 122 is additionally coupled to an input terminal of each of coincidence means 112 and 118 via logic negation circuit 113. The logic negation circuit may comprise conventional inverter means adapted to produce a binary l in response to a binary' supplied thereto and, conversely, to produce a binary 0 in response to a binary 1 supplied thereto. Coincidence means 118, which may be similar to aforedescribed coincidence means 117, includes a further input terminal coupled to transducer 123 and an output terminal coupled to coincidence means 117. One of ordinary skill in the art should appreciate that coincidence means 118 may be omitted, whereby inverter means 113 and transducer 123 may be coupled directly to respective input terminals of coincidence means 117. It may be observed that coincidence means 112 includes a third input terminal coupled in common relationship with appropriate input terminals of coincidence means 109 and OR circuit 115 to transducer 121. As has been described hereinabove, flip-flop means 110 is capable of assuming a first state in response to a binary 1 applied to the set input terminal thereof and a second state in response to a binary l applied to the reset input terminal thereof. Should a binary l be simultaneously applied to both the set and the reset input terminals, flip-flop means 110 is adapted to assume its first state. Hence, flip-flop means 110 may include conventional internal bias networks to provide for the aforementioned condition. Alternatively, the set input terminal may be coupled to the reset input terminal by the illustrated circuit comprised of inverter means 111 and coincidence means 116. In this configuration, flip-flop-means 110 assumes its first state in all instances where a binary 1 is applied to the set input terminal thereof.

The operation of. the elevator assembly and control means therefor will now be described. It will be .assumed, for purposes of explanation, that the illustrated apparatus is employedin an electrostatic reproduction machine. Furthermore, platform 101 is movable in an upward direction and a downward direction. Nevertheless, it should be clearly understood, that the bidirectionally movable platform may be displaced in a left-to-right configuration. When an operator elects to lower the platform 101 to its extreme downward position, switch means 125 is manually energized. This switch means may, therefore, be designated the elevator down switch. Energization of the elevator down" switch provides a channel from the source of energizing potential +V to the first input terminal of coincidence means 109 to supply a binary 1" thereat. If platform 101 has not yet attained its extreme downward position, transducer 121 supplies a binary 1" to the second input terminal of coincidence means 109. It is appreciated that, if the electrostatic reproduction machine admits of an operating condition, such as a print cycle, wherein the sheets of material stacked upon platform 101 are to'be supplied to the sheet transport mechanism to effect a proper operation of the machine, platform 101 must not be lowered. Hence, if this operating condition obtains, a binary 0 is applied to terminal 108 and coincidence means 109 is inhibited from supplying a binary 1 to the set input terminal of flip-flop means 110. However, when the electrostatic reproduction machine does not require the transport of sheets of material therethrough, a binary l is applied to terminal 108. Assuming the latter condition to prevail, each input terminal of coincidence means 109 is aupplied-with a binary l and, therefore, a binary l is applied to-the set input terminal of flip-flop means 110, thereby actuating the flip-flop means to assume its first state. It may be observed that the binary 1 produced by transducer 121, representing that platform 101 has not attained its extreme downward position, is also supplied to OR circuit 115 and thence to an input terminal of coincidence means 116. But the binary l produced by coincidence means 109 undergoesa logic negation by inverter means 111 to supply the other input terminal of coincidence means 116 with a binary 0." Thus, the reset input terminal of flip-flop means receives a binary 0.

The assumption'of its first state by flip-flop means 110 provides a binary 1 at the first outputterminal thereof. Since platform 101 has not attained its extreme downward position, coincidence means 112 is supplied with a binary l by transducer 121. Accordingly, two input terminals of coincidence means 112 are each supplied with a binary l If access door 107 is closed, transducer 122 produces a binary 0 which undergoes a logic negation by inverter means 113 to supply the third input terminal of coincidence means 112 with a binary 1 It is recognized that a binary l is now supplied to each input terminal of coincidence means 112 and, therefore, a first input binary l is applied to drive control means 106. it is recalled that drive control means 106 responds to the first input applied thereto to energize motor 104 whereupon platform 101 is driven in a downward direction. The energization of motor 104 is maintained while coincidence means 112 is supplied with a binary 1" at each input terminal thereof. Accordingly, the driving of platform 101 in a downward direction is terminated when flipflop means 110 is reset to assume its second state. Similarly, the driving of platform 101 in a downward direction is interrupted when transducer 122 senses that access door 107 is opened, whereupon a binary l is applied to inverter means 113. Finally, when platform 101 attains its extreme downward position, it is preferred that the energization of motor .104 be suspended. Hence, a binary O is supplied by transducer 121 to an input terminal of coincidence meansl12 when the transducer senses the presence of platform 101 in its extreme downward position.

An advantageous feature of the present invention is that platform 101 need not be driven to its extreme downward position in response to action inadvertently initiated by the operator. More particularly, if elevator down switch 125 is inadvertently energized, platform 101 will initially be driven downward; but the subsequent de-energization of elevator down" switch 125 will drive platform 101 upward to return to a proper sheet feeding position. Similarly, if, after intentionally energizing elevator down switch 125, the operator changes his mind, de-energization of the switch will return platform 101 to a proper sheet feeding position. Consequently, the time delay attendant to the driving of platform 101 between extreme positions is hereby avoided. The manner in which this is accomplished by the illustrated apparatus is now described.

It is recalled that the state assumed by flip-flop means 110 is effective to determine the direction in which platform 101 is driven. Thus, if flip-flop means 110 is set to assume its first state, coincidence means 112 is adapted to provide a first input to drive control means 106 whereby platform 101 is driven downward. Conversely, if the flip-flop means is reset to assume its second state, coincidence means 117 is adapted to provide a second input to drive control means 106 whereby platform 101 is driven upward. As has been described hereinabove, flip-flop means 110 is set to its first state in response to a binary 1 applied thereto by coincidence means 109, viz., when elevator down switch 125 is energized and whentransducer 121 senses that platform 101 has not attained its extreme downward position. It may be observed that the binary 1 produced by transducer 121, which is a condition precedent to the setting of flip-flop means 110 to its first state, is also applied to coincidence means 116 via OR circuit 115. When elevator down switch 125 is deenergized, coincidence means 109 applies a binary O to the set input terminal of flip-flop means 110 and to inverter means 111. The binary applied thereto is subject to a logic negation by inverter means 111 whereupon coincidence means 116 is provided with a binary l at each input terminal thereof. Accordingly, a binary l is now applied to the reset input terminal of flip-flop means .110 to reset the flip-flop means to its second state. Therefore, coincidence means 112 is deactuated and the first input is removed from drive control means 106. If, at the time of de-energizing elevator down switch 125, platform 101 had been displaced such that the top-most sheet stacked thereon does not admit of a proper position whereby it may be supplied to the sheet transport mechanism, coincidence means 118 is supplied with a binary 1" by transducer 123. Furthermore, if access door 107 remains closed, the binary 0 produced by transducer 122 is inverted by inverter means 113 and applied to coincidence means 118. Consequently, each of flip-flop means 110 and coincidence means 118 supplies coincidence means 117 with a binary l; the latter coincidence means now being effective to apply a binary I second input to drive control means 106. The drive control means 106 responds to the second input applied thereto to energize motor 104 whereupon platform 101 is driven in an upward direction. The platform will be continually driven upward unless, or until, flip-flop means 110 is set to assume its first state, i.e., elevator down" switch 125 is energized, or coincidence means 118 is deactuated. Thus, if an operator elects to open access door 107, the binary l produced by transducer 122 is. inverted by inverter means 113 and applied as a binary 0" to coincidence means 118. Also, if platform 101 is driven upward to assume a proper sheet feeding position, transducer 123 produces a binary 0 which is supplied to coincidence means 118.

It should now be readily apparent that the apparatus illustratively depicted and described herein requires the continual energization of elevator down switch 125 to drive the elevator assembly to an extreme downward position. The premature de-energization of such switch results in the return of the elevator assembly to a proper sheet feeding position. The opening of access door 107 by an operator, however, results in a restraint g of upward or downward movement by the elevator assembly. Another advantageous feature'of the present invention is the return of platform 101 to a proper sheet feeding position when the platform is displaced therefrom at a predetermined time subsequent to the completion of an operating cycle by the electrostatic reproduction machine. When a reproducing operation is completed by the electrostatic reproduction machine, that is, after the finished copy, or the last of multiple copies, of an original document is discharged from the machine, a quiescent condition is maintained for a predetermined interval of time. During this interval, an operator may execute appropriate functions to initiate a further reproducing operation. If, however, no further action is taken, a binary l is produced by suitable means, not shown, and applied to terminal 114 at the expiration of the predetermined interval. This binary l is supplied to OR circuit 115 and thence to coincidence means 116. Should the elevator down switch not be energized, or should platform 101 assume its extreme downward position, coincidence means 109 provides a binary 0" to inverter means 1 1 1 and a binary l is applied to each input terminal of coincidence means 116. Accordingly, flip-flop means 110 is reset to assume its second state and coincidence means 117 is adapted to supply a second input to drive control means 106. Platform 101 is therefore driven upward to be positioned in a proper sheet feeding position.

In the design of the present invention, it is assumed that an operator will effect the loading of the elevator assembly with sheets of material to enable the electrostatic reproduction machine to utilize said sheets in the production of copies of an original document. It is further assumed that access door 107 will be opened to permit an operator to accomplish this function. Since the loading of the elevator assembly with sheets of material is advantageously executed when the assembly assumes its extreme downward position, it is preferred to return the elevator assembly to a proper sheet feeding position once the access door is closed. Transducer 122 senses the opening of access door 107 by an operator to provide a binary l to an input terminal of coincidence means 116 via OR circuit 115. It is recognized that if platform 101 assumes its extreme downward position, or if elevator down switch 125 is not energized, coincidence means 1 16 is provided with a binary 1" at its other input terminal. Accordingly, flip-flop means 110 is reset to its second state to apply a binary 1 to an input terminal of coincidence means 117. Upon closing access door 107, the binary produced by transducer 122 is inverted by inverter means 113 and applied as a binary 1 to an input terminal of coincidence means 118. Coincidence means 118 is effective to apply a binary l to the other input terminal of coincidence means 117 because platform 101 is not, at this time, disposed in a proper sheet feed- .ing position. Consequently, coincidence means 117 supplies a binary 1 second input to drive control means 106 to the'reby return platform 101 to a proper sheet feeding position. After a predetermined number of sheets 102 are fed to the sheet transport mechanism with which the present invention is utilized, transducer 123 produces'a binary 1 representing that the topmost sheet is not in proper position. Coincidence means 118 thus applies a binary l to coincidence means 117 and platform 101 is indexed upward until the transducer now produces'a binary 0. ln this manner, platform 101 is maintained in a proper sheet feeding position.

It should be appreciated that the condition may obtain wherein an operator has effected the lowering of platform 101 to its extreme downward position by energizing elevator down" switch 125, but now desires the immediate return of the platform to its proper sheet feeding position whereby an operating cycle of the electrostatic reproduction machine may be commenced. it is recalled that platform 101 is returned to its proper sheet feeding position at a predetermined time subsequent to the completion of a previous operating cycle, or when an operator effects the opening and closing of access door 107. The platform may also be returned to its proper sheet feeding'position by energizing an operating cycle initiation switch, here depicted as print switch 124. Manual energization of print switch 124 by an operator provides a channel from the source of energizing potential +V to OR circuit 115 to supply a binary l thereto. Flip-flop means 110 may be reset to assume its second state in the now understood manner, whereby coincidence means 117 applies a binary 1" second input to drive control means 106. Platform 101 may thus be driven upward to assume its proper sheet feeding position.

It should now be readily appreciated from the foregoing description that the illustrated apparatus tends to bias platform 101 to normally assume a proper sheet feeding position. This apparent biasing may be overcome by the continual energization of switch means 125. De-energization of switch means 125 results in the displacement of the platform in an upward direction. Furthermore, although platform 101 has been specifically described as movable in upward and downward directions, it is recognized that the platform is bidirectionally movable and may, if desired, be displaced in lateral directions. Hence platform 101 may be driven to an extreme first position when switch means 125 is energized and to a proper sheet feeding position when the switch means is de-energized. Moreover, the control apparatus illustrated in FIG. 2 is intended to be input terminal adapted to be supplied with signals representing the operating condition of the electrostatic reproduction machine or such other machine with which the present invention may be utilized. Similarly, coincidence means 117 and 118 may be replaced by a single coincidence means having three input terminals. Likewise, the signals produced by eachof the three transducers 121-123 are reversible. Hence, a binary 1 may be produced by transducer 121 when platform 1101 assumes'an extreme first position; a binary 1, may be produced by transducer 122 when access door 107 is closed; and a binary 1" may be produced by transducer 123 when platform 101 assumes a proper sheet feeding position. It is understood that minor changes should be effected in the illustrated control apparatus in a manner that is compatible with these aforenoted modifications. It is now apparent that the foregoing and various other changes and modifications in form and details may be made without departing from the spirit and scope of the invention. It is therefore intended that the appended claims be interpreted as including all such changes and modifications.

What is claimed is:

1. In combination with a bi-directionally movable platform for supporting a stack of sheets of material adapted to be 'fed to an operating device, control means for controlling the operation of platform driving means, comprising: direction determining means comprising flip-flop means for producing a first signal to drive said platform in a first direction and a second signal to drive said platform in a second direction whereby said first and second signals are produced when said flip-flop means assumes first and second states, respectively;

first sensing means for sensing when said platform assumes a first extreme position; first means coupled to said first sensing means and responsive to the energization of a selecting switch for actuating said direction determining means to produce said first signal when said platform is not in said first extreme position; second means selectively responsive to the deenergization of said selecting switch and to the operating condition of said operating device for actuating said direction determining means to produce said second signal; and drive'control means coupled to said direction determining means and responsive to said first and second signals to drive said platform driving means in a first and second direction, respectively. 2. The combination of claim 1 wherein said first means comprises coincidence means having a first inputcoupled to said selecting switch, a second input coupled to said first sensing means and an output coupled to said flip-flop means for driving said flip-flop means into its first state when said selecting switch is energized and said platform is not in its first extreme position.

3. The combination of claim 2 wherein said second means comprises:

OR circuit means having a first input coupled to said first sensing means, a second input adapted to be supplied with signals representing the operating condition of said operating device and an output coupled to said flip-flop means for driving said flipflop means into its second state when said platform is not in its first extreme position or said operating device admits of predetermined operating conditions; and

means for preventing said flip-flop means from being driven into its second state when said coincidence means is energized.

4. The combination of claim 2 wherein said means for coupling comprises further coincidence means having a first input coupled to said second sensing means, second input coupled to said flip-flop means and an output coupled to said drive control means.

5. In an electrostatic reproduction machine wherein a viewable image is formed on sheets of material supplied by an elevator assembly upon which said sheets are stacked, apparatus for regulating the position of said elevator assembly in response to operatorperformed functions, comprising:

direction determining means for producing a first signal to drive said elevator assembly in a downward direction and a second signal to drive said elevator assembly in an upward direction;

first sensing means for sensing when said elevator assembly assumes an extreme downward position; first means comprising AND gate means having a first input coupled to an elevator down switch and a second input coupled to said first sensing means for producing said first signal when said elevator down switch is operated and said elevator assembly is not in said extreme downward position;

second means selectively responsive to the release of said elevator down" switch and to signals representing predetermined operating conditions of said electrostatic reproduction machine for actuating said direction determining means to produce said second signal; and

elevator drive means coupled to said direction determining means and responsive to said first and sec I ond signals for driving said elevator assembly in a downward and an upward direction, respectively.

6. The apparatus of claim 5 wherein said second means comprises OR circuit means having a first input coupled to said first sensing means, a second input adapted to be supplied with a signal generated at a predetermined time subsequent to the completion of an operating cycle by said electrostatic reproduction machine, a third input coupled to an operating cycle initiation switch and a fourth input adapted to be supplied with a signal generated in response to a predetermined operator-initiated action for producing a second actuating signal.

7. The apparatus of claim 6 wherein said direction determining means comprises flip-flop means having a first input coupled to said AND gate means and responsive to said first actuating signal to assume a first state and a second input coupled to said OR circuit means and responsive to said second actuating signal to assume a second state, said flip-flop means being inhibited from assuming said second state when said first actuating signal is applied to said first input.

8. The apparatus of claim 7 further including:

second sensing means for sensing when said elevator assembly is in a proper position for supplying said sheets of material stacked thereon; and

further AND gate means having a first input coupled to said flip-flop means and a second input coupled to said second sensing means for supplying said elevator drive means with an energizing signal to drive 5 said elevator assembly in an upward direction when said flip-flop means assumes its second state and said elevator assembly is not in said proper position.

9. The apparatus of claim 8 wherein said fourth input of said OR circuit means is coupled to switch means adapted to be closed when an access door of said elevator assembly is closed, said access door providing access by an operator to said elevator assembly to effect the loading and unloading of said elevator assembly with sheets of material.

10. In an electrostatic reproduction machine wherein an image is formed on sheets of material supplied from an elevator assembly upon which said sheets are stacked, apparatus for regulating the position of the elevator assembly in response to machine and operatorperformed functions, comprising:

elevator drive means for driving said elevator assembly between an extreme upper position and an extreme lower position; sheet sensing means responsive to the position of the top sheet on the elevator assembly for energizing said elevator drive means to move said elevator assembly in an upward direction as the sheet supply is depleted during a machine operating cycle to maintain the top sheet in a position to be fed through the reproduction machine;

an elevator down" switch adapted for operation by the machine operator for overriding said sheet sensing means to energize said elevator drive means to move said elevator assembly in a downward direction; and

control means adapted to prevent energization of said elevator drive means by said elevator down switch during a machine operating cycle.

11. Apparatus for regulating the position of the elevator assembly in an electrostatic reproduction ma chine according to claim 10 further including elevator sensing means for sensing when said elevator assembly assumes an extreme downward position in response to operation of the elevator down switch; and

time delay means responsive to said elevator sensing means to maintain said elevator assembly in the extreme downward position after the elevator down switch is released to prevent immediate upward movement thereof in response to the absence of sheets of said sheet sensing means.

12. Apparatus for regulating the position of the elevator assembly in an electrostatic reproduction machine according to claim 11 further including means for overriding said time delay means upon the start of a machine operating cycle to allow said elevator assembly to assume the required position for feeding sheets through the reproduction machine.

13. Apparatus for regulating the position of the elevator assembly in an electrostatic reproduction machine according to claim 12 wherein the electrostatic reproduction machine includes an elevator assembly cover for enclosing the elevator assembly, said apparatus further including cover interlock means associated with said cover to de-energize said elevator assembly when said cover is opened, said means for overriding said time delay means further including means associated with said cover interlock means for overriding said time delay means when said cover is opened and subsequently closed. 

1. In combination with a bi-directionally movable platform for supporting a stack of sheets of material adapted to be fed to an operating device, control means for controlling the operation of platform driving means, comprising: direction determining means comprising flip-flop means for producing a first signal to drive said platform in a first direction and a second signal to drive said platform in a second direction whereby said first and second signals are produced when said flip-flop means assumes first and second states, respectively; first sensing means for sensing when said platform assumes a first extreme position; first means coupled to said first sensing means and responsive to the energization of a selecting switch for actuating said direction determining means to produce said first signal when said platform is not in said first extreme position; second means selectively responsive to the de-energization of said selecting switch and to the operating condition of said operating device for actuating said direction determining means to produce said second signal; and drive control means coupled to said direction determining means and responsive to said first and second signals to drive said platform driving means in a first and second direction, respectively.
 2. The combination of claim 1 wherein said first mEans comprises coincidence means having a first input coupled to said selecting switch, a second input coupled to said first sensing means and an output coupled to said flip-flop means for driving said flip-flop means into its first state when said selecting switch is energized and said platform is not in its first extreme position.
 3. The combination of claim 2 wherein said second means comprises: OR circuit means having a first input coupled to said first sensing means, a second input adapted to be supplied with signals representing the operating condition of said operating device and an output coupled to said flip-flop means for driving said flip-flop means into its second state when said platform is not in its first extreme position or said operating device admits of predetermined operating conditions; and means for preventing said flip-flop means from being driven into its second state when said coincidence means is energized.
 4. The combination of claim 2 wherein said means for coupling comprises further coincidence means having a first input coupled to said second sensing means, a second input coupled to said flip-flop means and an output coupled to said drive control means.
 5. In an electrostatic reproduction machine wherein a viewable image is formed on sheets of material supplied by an elevator assembly upon which said sheets are stacked, apparatus for regulating the position of said elevator assembly in response to operator-performed functions, comprising: direction determining means for producing a first signal to drive said elevator assembly in a downward direction and a second signal to drive said elevator assembly in an upward direction; first sensing means for sensing when said elevator assembly assumes an extreme downward position; first means comprising AND gate means having a first input coupled to an ''''elevator down'''' switch and a second input coupled to said first sensing means for producing said first signal when said ''''elevator down'''' switch is operated and said elevator assembly is not in said extreme downward position; second means selectively responsive to the release of said ''''elevator down'''' switch and to signals representing predetermined operating conditions of said electrostatic reproduction machine for actuating said direction determining means to produce said second signal; and elevator drive means coupled to said direction determining means and responsive to said first and second signals for driving said elevator assembly in a downward and an upward direction, respectively.
 6. The apparatus of claim 5 wherein said second means comprises OR circuit means having a first input coupled to said first sensing means, a second input adapted to be supplied with a signal generated at a predetermined time subsequent to the completion of an operating cycle by said electrostatic reproduction machine, a third input coupled to an operating cycle initiation switch and a fourth input adapted to be supplied with a signal generated in response to a predetermined operator-initiated action for producing a second actuating signal.
 7. The apparatus of claim 6 wherein said direction determining means comprises flip-flop means having a first input coupled to said AND gate means and responsive to said first actuating signal to assume a first state and a second input coupled to said OR circuit means and responsive to said second actuating signal to assume a second state, said flip-flop means being inhibited from assuming said second state when said first actuating signal is applied to said first input.
 8. The apparatus of claim 7 further including: second sensing means for sensing when said elevator assembly is in a proper position for supplying said sheets of material stacked thereon; and further AND gate means having a first input coupled to said flip-flop means and a second input coupled to said second sensing means for supplying said elevator drive means with an eneRgizing signal to drive said elevator assembly in an upward direction when said flip-flop means assumes its second state and said elevator assembly is not in said proper position.
 9. The apparatus of claim 8 wherein said fourth input of said OR circuit means is coupled to switch means adapted to be closed when an access door of said elevator assembly is closed, said access door providing access by an operator to said elevator assembly to effect the loading and unloading of said elevator assembly with sheets of material.
 10. In an electrostatic reproduction machine wherein an image is formed on sheets of material supplied from an elevator assembly upon which said sheets are stacked, apparatus for regulating the position of the elevator assembly in response to machine and operator-performed functions, comprising: elevator drive means for driving said elevator assembly between an extreme upper position and an extreme lower position; sheet sensing means responsive to the position of the top sheet on the elevator assembly for energizing said elevator drive means to move said elevator assembly in an upward direction as the sheet supply is depleted during a machine operating cycle to maintain the top sheet in a position to be fed through the reproduction machine; an ''''elevator down'''' switch adapted for operation by the machine operator for overriding said sheet sensing means to energize said elevator drive means to move said elevator assembly in a downward direction; and control means adapted to prevent energization of said elevator drive means by said ''''elevator down'''' switch during a machine operating cycle.
 11. Apparatus for regulating the position of the elevator assembly in an electrostatic reproduction machine according to claim 10 further including elevator sensing means for sensing when said elevator assembly assumes an extreme downward position in response to operation of the ''''elevator down'''' switch; and time delay means responsive to said elevator sensing means to maintain said elevator assembly in the extreme downward position after the ''''elevator down'''' switch is released to prevent immediate upward movement thereof in response to the absence of sheets of said sheet sensing means.
 12. Apparatus for regulating the position of the elevator assembly in an electrostatic reproduction machine according to claim 11 further including means for overriding said time delay means upon the start of a machine operating cycle to allow said elevator assembly to assume the required position for feeding sheets through the reproduction machine.
 13. Apparatus for regulating the position of the elevator assembly in an electrostatic reproduction machine according to claim 12 wherein the electrostatic reproduction machine includes an elevator assembly cover for enclosing the elevator assembly, said apparatus further including cover interlock means associated with said cover to de-energize said elevator assembly when said cover is opened, said means for overriding said time delay means further including means associated with said cover interlock means for overriding said time delay means when said cover is opened and subsequently closed. 